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Module 1: The Phases of Aircraft Design

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House of Quality Chart for HALE UAV

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Lecture – 11

Examples of House of Quality for HALE UAV

Let us have a look at an example of the house of quality for a high altitude long endurance unmanned aerial vehicle or HALE UAV. At this stage, I would like to confirm that you have already watched the video clips where we described the requirements capture and HoQ. So if you have not done that I would recommend that you watch those video clips before you watch this example because here we will not be explaining or describing the working of HoQ, we will just show you how it is applied to an example of a high altitude long endurance unmanned aerial vehicle.

Why QFD is important? This graph shows how the cost of the changes increases as we proceed further and further in the cycle of completing the product. So during the concept design stage, the cost of changes is very low. During design and development, it is slightly higher and that is the ideal time for any changes or any modifications to be done in the design, but as you go into design validation the cost of changes rises.

And when we go to the production design stage and there if you make any major changes that is the worst time for change because the cost of change is very high. So therefore in the initial phases, it is very important to get it right and to make it work so that later on we do not have to really regret and incur heavy expenditure.

So, just a quick recap that first you list down the customer needs in the box on the left hand side and then you assign the priorities to these needs. So this information comes from a survey of the customer requirements and then you have the design team decides which design features are to be provided in a candidate design. So they fill up this design features box.
Then looking at the competition and looking at what aims they would like to follow, some target values for the design features that you are going to investigate have to be given in the bottom box.

There is no point in exceeding these values too much because then something else will be compromised okay and then you fill in the design features matrix. After that you calculate the priorities and then after the priorities are calculated, the rooftop is used to fill in the feature correlation matrix because if there are two design features which strongly support each other
that is great.

So there should be a lot of dark dots and open dots in the top and the crosses and you know stars are very bad because that means the features are contrary to each other or contradicting each other. Finally what you do is depending on the design feature priority that you calculate you can rank the design features and then you can drop off the features which have low rank
and continue further with the features that have high ranks okay.

So what you do, then you repeat the whole process. Now what you do is use the high-ranking design features as the customer needs and then you go one level down and try to address what features to provide to address these needs. So on and so forth you can do and continue working further till you reach the end of the design.

So if you look at the Clausing four-level QFD model which is also explained in the presentation. First the house of quality level one would contain the customer attributes and the engineering characteristics of the product have to be studied. Now with this, the characteristics that score a very high rank then become the requirements and the parts characteristics are to be determined based on which of them are going to address those requirements better.

Once you decide which part characteristics are important, you use them as the design as the customer attributes and now you look at the key process operations. So the process planning comes into play. So you identify the key processes which help you achieve the parts characteristics which help you achieve the engineering characteristics and finally the key processes then go into the production planning requirement.

So this is the four level house of quality where we convey the customers voice through to manufacturing okay. The source of this is a very interesting article in Harvard Business Review by Hauser and Clausing published way back in 1988.

So the first of the four-level models looks at the voice of the customer and converts the principal performance parameters. Then it uses the performance parameters as needs to get the parts characteristics that is used as the need to get the manufacturing processes and that is used as the need to get the manufacturing controls. So we will now see how the house of quality as studied in this particular thesis is used in this four level.

The example that he has taken is the Global Hawk UAV. Global Hawk is a very well known high altitude long endurance UAV and in this example a critical evaluation of the design of the HALE UAB was carried out.

Now there are many many other ways in which the HoQ can be given as a nomenclature. So customer needs are of course the prime and they come in the top always okay. So customer needs are always there which are there in this vertical box. Then you have the planning matrix where you assign varieties of the designs okay. So the customer actually tells us which
particular attribute is more important and also assigns the weightage to that.

Then we have the technical responses or essentially the targets which are obtained either from a study of the competition or based on our own assessment of what targets we would like to provide. Then you fill in the relationships in the design feature matrix. Then you do technical correlations on the top that is the feature correlation and finally you have the technical response priorities or the design feature priorities.

So you can notice it is only a difference in the terminology, otherwise you know whether you say that you assign priority to needs or whether you say fill in the planning matrix is the same thing, whether you say decide design prior features or design responses is the same okay.

Like that so the logical sequence is very straightforward. First thing you do is to identify the voice of the customer, look at the wants and the needs and for this you have to look at the RFP, the request for proposal from the customer. Then you look at the planning matrix, so you can look at the market data, look at some strategic goals that the company may have and then you do the rank ordering of the needs.

Sometimes this information comes from the customer directly or from some other market survey and then you fill in the design features or you decide which design features you will investigate. Then you do the mapping between design parameters and customer needs. Then you do the interrelationships between the design parameters both positive and negative interrelations. Notice that in the central box where you do the mapping between the design
parameters the customer needs.

You normally do not look for any negative correlation, you ignore all negative correlations and focus only on the positive correlations because here our aim is to decide which one is better. So you can do it purely by finding which has got a higher rank. If you start using negative numbers here, then you might actually cause some confusion because you know it is possible that two features which have negative numbers can cancel the one positive feature,
so we do not do that.

We just say that we look only at positive relationships here and negative ones are on the top where we look at the interrelationships, but here we look at negative and positive both and finally based on the numbers that you fill in this particular matrix you can prioritize the design parameters.

So let us first look at the level 1 QFD which is the customer's voice transformation into the performance parameters. So the voice of the customer essentially means understanding the
customer attributes or CAs which is what okay. So needs and wants, actually you have to convert whats into needs and wants and this is accomplished using the process of requirements capture which has already been explained through a separate video clip, so I hope you have seen that.

Using this voice of the customer and whats, you arrive at the performance parameter that is the hows okay. So in level 1 QFD the whats which are the customer attributes are converted into hows which are the design features.

So how do you convert whats into hows okay? So from the baseline UAV you look at some key design parameter. There are some dimensions the wingspan, the wing reference area, the fuselage length and the maximum diameter. There is gross weight of the aircraft. Then you have the zero left drag coefficient, the wing loading, some airfoil parameters like the
maximum thickness to chord ratio, the maximum lift coefficient, the maximum increment in the Cl because of the flaps, etc.

Then you having wing aspect ratio, Oswald efficiency factor. There are some speeds, the cruise speed and the maximum speed and then there are thrust to weight ratios and the SFC. So these are the key design parameters from the baseline UAV.

Their numerical values have been taken and then what you do is with respect to each of these requirements, you start correlating them into performance parameters. So CD is one of the important performance parameter, TR is the thrust required in level flight, rate of climb maximum which is available as a ratio of either you can use an expression like this or you can convert this into just T cube by W square okay.

Then the range which could also be simplified, this is for the FPS system that is why these numbers are appearing okay and from here you can simplify it further. This is the endurance, so 24 hour endurance is needed so that is obtained by the Breguet range and endurance equation and because it is a jet UAV you are using this 0.866 times for the L by D max value.
For the ceiling you have an expression that correlates parameters like aspect ratio e CD0 and T by W with the maximum ceiling.

This is the formula that correlates the landing, liftoff distance, take off ground roll with the parameters during takeoff. You can simplify it by neglecting some of the terms okay and then you have the load factor n and the turn rate omega okay. So these are the 10 performance parameters.

So what you do is you do a rough order of magnitude analysis that means to correlate between changes. For example a small change in Cl how much will it change in the various performance parameters, you can do this by making order of magnitude analysis, also called as figure of merit analysis. So what you do is you keep all other house constant, take every every one how, every one design parameter and see the effect on each of the whats or the requirements.

So let us look at three parameters. So we look at only TSFC, thrust to weight ratio and wing aspect ratio. The baseline value is 0.6 per hour, 0.33 and 25. So what we need to see is okay keeping everything else constant if the powerplant TSFC is changed, both positive and negative, how does it affect the values.

So what you do for that is basically you can notice that if you look at for correlations for Ct =0.6, so if you look at the first parameter that is the thrust coefficient okay that is the thrust SFC. So Ct = 0.6 you notice that only these two expressions contain the Ct terms that is the endurance and range, everywhere else the SFC does not matter.

So then what you do is to achieve those good quality components, you then go to a component level where you can take one component and try to arrive at various new fixtures which can be created to address the requirements. So we have looked at the manufacturing processes and it was very clear that use of composites was a big help, so therefore so many processes which are related to composites have come in, but also we have brought in
something like powder metallurgy, precision forging, extrusions okay, pultrusion, hot stamping these are also some other methods by which it can be done.